Transducer apparatus



United States Patent TRANSDUCER APPARATUS Cosler D: Knight, Lake Zurich, Ill., assignor to Zenith Radio Corporation, a corporation of Delaware Filed Dec. 3, 1958, Ser. No. 778,017 4 Claims. (Cl. 179100.41)

This invention is directed to transducer apparatus and more particularly to such apparatus which provides two audible output signals which together create the illusion of position and/ or movement.

The conventional phonograph system, in which a single channel of information is derived from a record groove and reproduced through a single sound-translating system, is well known. Recently a dual-channel system has been made commercially available, which system gives an apparent indication of position and/or movement of the source originally used to impress the information on the record; this illusion or effect has been termed stereophonic sound) In such a system, two spaced-apart microphones are utilized in recording. The signal picked up by each microphone is separately translated and amplified and, when subsequently reproduced through two separate and'properly positioned speaker systems, the eifect is similar to that which would be heard if a multiplicity of sound sources were positioned between the speaker systems. A method has been developed for impressing both channels of information in a single record groove, and

for subsequently reproducing the separate channels from thegroove to achieve a stereophonic effect.

To minimize cross talk between channels and degradation of the individual channel signals, one approach includes matrixing of the separate channel signals derived from the record groove to provide sum and difference signals, rather than merely right and left channels. Right and left refer to the physical placement of the microphones or speakers relative to a reference location. The sum and diiference channels are amplified and subsequently matrixed to provide separate left and right channel signals for each of the two output systems.

I One type of pickup arrangement includes two separate transducer assemblies physically positioned perpendicular to each other for mechanical displacement by a common needle riding in the groove of a stereophonic record. This arrangement is suitable for use with a record having two separate channels of information impressed thereon by variations of the depth of either wall of the V-shaped groove. Each of the two transducer assemblies has two outputorv signal-translating electrodes. To provide matrixing of the left and right channel signals, it has been conventional practice to couple a series-connected pair of voltage divider resistors in parallel with one of the transducer assemblies; the mid-point of the resistors is connected to one electrode of the remaining assembly, the I other electrode of which is a common output connection for the pickup and'matrixing arrangement. In addition to this common connection, second and third output connections are attached to the opposite signaltranslating electrodes of the first assembly. To incorporate the voltage divider resistances in the matrixing circuit, it'is necessary that four terminals be provided for connection to the signal-translating electrodes of the two transducer assemblies. The provision of four terminals in the cartridge is both difficult and expensive.

It is aniobject of this invention to provide a simplified pickup and matrixing arrangement for stereophonic sound reproducing systems.

It is another object of the invention to provide a simplified arrangement which reduces the number of terminals required in the cartridge itself.

It is a further. object of the invention to provide such a simplified arrangement which obviates the requirement for a separate voltage divider circuit connected across one of the transducers.

Yet another object of the invention is to provide such an arrangement without introducing additional circuit components or adding extra electrodes to the conventional transducer assemblies.

A stereophonic pickup and matrixing arrangement constructed inaccordance with the invention includes a first transducer assembly comprising a body of piezoelectric material, with a pair of signal-translating electrodes affixed to different surfaces of this body. A pair of output terminals is connected to these electrodes respectively and a common electrode is disposed on another surface of the body, and constitutes-with each of the signaltranslating electrodes a transducing element. A second transducer assembly includes a body of piezoelectric material and a pair of signal-translating electrodes aflixed to diiferent surfaces thereof. Means are provided for coupling the common electrode to one of the signal-- translating electrodes of the second transducer assembly a and a third output terminal is connected to one of the electrodes of the second transducer assembly.

The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a block diagram, partly in schematic form, illustrating a stereophonic sound-reproducing system which employs sum and difference channels;

FIGURE 2 is an illustrative showing useful in understanding the operation of the invention;

FIGURE 3 is a sectional view illustrating an alternate construction of. the piezoelectric material depicted in FIGURE 2;

FIGURE 4 is a partial schematic diagram illustrating a prior art device; and

FIGURE 5 is a partial schematic diagram which portrays one embodiment of the invention.

The sound-reproducing system of FIGURE 1 includesv a turntable 10 connected to a motor 11, to which is connected a power cord 12 terminating in a plug 13 for insertion in a conventional power receptacle (not shown). The stereophonic pickup and matrixing arrangement 14 is positioned to engage stereophonic record 15. Three different output leads from pickup and matrixing arrangement 14 are separately connected to the output terminals 16, 17 and 18. Terminal 16 is in turn connected to one end of a load resistor 20, the other end of which is connected both to a point of reference potential such as ground and to one input terminal of amplifier 21. The other input terminal of amplifier 21 is directly connected to terminal 16. A similar connection is made from terminal 17 over load resistor 22 to amplifier 23; terminal 18 is connected to ground.

One of the output terminals of each of amplifiers 21 and 23 is connected to ground, and the remaining output terminals are connected to the input side of a matrixing arrangement 24, the output terminals of which are in turn connected to amplifiers 25 and 26. These amplifiers are separately coupled to sound-translating systems 27 and 28 which may be loudspeakers or other transducers.

In operation, energization of motor 11 effects angular displacement of turntable 10 and record 15. The undulations in the walls of the record grooves cause movement of the needle of pickup and matrixing arrangement 14 which provides two separate electrical signals, in a manner to be described hereinafter. The two separate signals are matrixed to provide a first composite signal,

indicative of a summation of the left and right channel I signals (L+R), at terminal 16. The diflerence signal of the left and right channel signals (LR) is translated over terminal 17, and terminal 18 is utilized as a reference. The L+R signal is'amplified in amplifier 21 and applied to one input of matrix 24; the-amplified L-R signal is also applied to the input side of matrix 24. In a manner well known and understood by those skilled in the art, the sum and difference signals are matrixed and at the output side of matrix 24 only the left and right channel signals appear. These separate channel signals are respectively amplified in amplifiers 25 and 26 and translated into audio-frequency variations in the speaker systems 27 and 28.

A portion of the pickup and matrixing arrangement 14 is illustrated in FIGURE 2. As there shown, this portion includes separate transducer assemblies 35 and 36, each of which comprises a body of piezoelectric material. For example, transducer assembly 35 may include a body of piezoelectric material, such as one of the well known polarized ceramics, with a pair of signal-translating electrodes 37 and. 38 afiixed to different surfaces of this body. A common electrode 40 is disposed on another surface and constitutes with each of electrodes 37 and 38 a separate transducing element. The other transducer assembly 36 (FIGURE 2) also includes signal-translating electrodes 47 and 48 on different surfaces thereof.

The manner in which such a body may be formed and polarized is now well known and understood. For example, the body 35 may in fact comprise two distinct ceramic pieces separated by a solid plate-like electrode 40 with the signal-translating electrodes 37 and 38 affixed to the outer surfaces as shown. In such a construction electrode 40 is conventionally utilized in the application of the polarizing fields after construction of the dimorph assembly.

Of course, the transducer assembly 35 may consist of a unitary ceramic body 42, as shown in FIGURE 3, in which the signal-translating electrodes 43 and 44 are affixed to the outer surfaces. In this construction, however, the common electrode 45 is provided by a plurality of longitudinal holes which are either filled or coated on the interior walls with conductive material; the solid or hollow cylinders thus formed are connected together externally. Thus electrode 45 can be utilized to effect polarization in exactly the same manner as the solid electrode 40 of FIGURE 2.

Because the transducer assemblies may take any of a multiplicity of forms, transducer assembly as used herein and in the appended claims is deemed to include all constructions where one or more associated elements effectively functions as a transducer assembly, ,notwithstanding that such element or associated elements may physically comprise only a portion of some integral structure.

Although transducer assemblies 35 and 36 are actually perpendicular to each other as illustrated in FIGURE 2, this showing has been altered in FIGURE 4 to portray more clearly the prior art electrical circuit connections. As there shown, the signal-translating electrodes 37 and 38 associated with the left channel transducer assembly 35 are connected to opposite terminals of a series-connected voltage divider arrangement including resistors 50 and 51. The mid-point or common junction of the voltage divider arrangement is connected to signal-translating electrode 47 of the right channel transducer assembly 36; the other signal-translating electrode 48 of assembly 36 is connected to the ground or reference terminal 18. This matrixing arrangement provides the sum channel signal (L+R) at the upper end of resistor 50 which is connected to output terminal 16, and the difference channel signal (LR) at the lower end of resistor 51 which is connected to output terminal 17. This construction is difiicult and expensive to realize because four terminals (two for each transducer assembly) must be inserted in a small cartridge space to provide for connection of the voltage divider resistors.

In accordance with the present invention, the signaltranslating electrode 47 of the right channel transducer 36 is connected directly to the common electrode 40 of the left channel transducer 35, as shown in FIGURE 5. This construction obviates both the exacting labor and extra space required to place a fourth terminal in the pickup itself. There is an additional economy because the two voltage divider resistors are also eliminated. No additional processing step is required to insert common electrode 40; this is done prior to the time the completed transducer assembly is polarized. Thus the economy and space saving consequent upon the practice of the invention are manifest.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made therein with out departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover 'all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. A stereophonic pickup and matrixing arrangement comprising: a first transducer assembly comprising a body of piezoelectric material, a pair of signal-translating electrodes affixed to different surfaces of said body, a pair of output terminals connected to said electrodes respectively, and a. common electrode disposed on another surface and constituting with each of said signaltranslating electrodes a transducing element; a second transducer assembly comprising a body of piezoelectric material and a pair of signal-translating electrodes afiixed to different surfaces thereof; means for coupling said common electrode to one of the signal-translating electrodes of said second transducer assembly and a third output terminal connected to one of said electrodes of said second assembly.

2. A stereophonic pickup and matrixing arrangement comprising: a first transducer assembly comprising a body of piezoelectric material, 'a pair of signal-translating electrodes affixed to different surfaces of said body, a pair of output terminals connected to said electrodes respectively, and a common electrode disposed on another surface and constituting with each of said signaltranslating electrodes a transducing element; a second transducer assembly disposed substantially perpendicular to said first assembly, comprising a body of piezoelectric material and a pair of signal-translating electrodes affixed to different surfaces thereof; means for coupling said common electrode to one of the signal-translating electrodes of said second transducer assembly and a third output terminal connected to one of said electrodes of said second assembly.

3. A stereophonic pickup and matrixing arrangement comprising: a first transducer assembly comprising a pair of ceramic pieces of piezoelectric material, a pair of signal-translating electrodes affixed to the outer surfaces of said pieces, a pair of output terminals connected to said electrodes respectively, and a common electrode disposed between said pieces on the inner surfaces thereof and constituting with each of said signal-translating electrodes a transducing element; a second transducer assembly comprising a body of piezoelectric material and a pair of signal-translating electrodes afiixcd to different surfaces thereof; means for coupling said common electrode to one of the signal-translating electrodes of said second transducer assembly and a third output terminal connected to one of said electrodes of said second assembly.

4. A stereophonic pickup and matrixing arrangement comprising: a first transducer assembly comprising a body of piezoelectric material, a pair of signal-translating electrodes affixed to different surfaces of said body, and a third output terminal connected to said electrodes respectively, and a common electrode comprising a plurality of conductive cylindrical elements disposed on another surface and constituting with each of said signaltranslating electrodes at transducing element; a second transducer assembly comprising a body of piezoelectric material and a pair of signal-translating electrodes affixed to difierent surfaces thereof; means for coupling said common electrode to one of the signal-translating electrodes of said second transducer assembly and a third 10 output terminal connected to one of said electrodes of said second assembly.

References Cited in the file of this patent UNITED STATES PATENTS 

